1) 3x² - 12 = 3(x² - 4) = 3(x - 2)(x + 2)
2) 2a² + 4ab + 2b² = 2(a² + 2ab + b²) = 2(a + b)²
3) -a² - 2a - 1 = -(a² + 2a + 1) = -(a + 1)²
4) 18a² - 27ab + 14ac - 21bc = 9a(2a - 3b) + 7c(2a - 3b) = (9a + 7c)(2a - 3b)
5) 10x² + 10xy + 5x + 5y = 10x(x + y) + 5(x + y) = 5(2x + 1)(x + y)
6) -28ac + 35c² - 10cx + 8ax = 7c(5c - 4a) - 2x(5c - 4a) = (7c - 2x)(5c - 4a)
7) 6a² - 3a + 12ba = 3a(2a + 4b - 1)
8) x² - y² + 2x + 2y = (x - y)(x + y) + 2(x + y) = (x - y + 2)(x + y)
9) 8x² - 2y² = 2(4x² - y²) = 2(2x - y)(2x + y)
10) (x - 4)² - 9x² = (x - 4 - 3x)(x - 4 + 3x) = (-2x - 4)(4x - 4) = -8(x + 2)(x - 1)
11) (2x - y)² - (x + 3y)² = (2x - y - x - 3y)(2x - y + x + 3y) = (x - 4y)(3x + 2y)
12) 25x² + 20xy + 4y² = (5x + 2y)²